1. Technical Field
The present invention relates to a method for producing a carburized part by carburizing a steel member under a vacuum.
2. Background Art
Carburization treatment for improving strength of a surface of steel materials is conventionally performed by a method such as gas carburization and vacuum carburization. For example, in gas carburization, as a method for improving a carburizing property by a preliminary oxidation, a method for carburizing a high-alloy steel after a preliminary oxidation (Japanese Unexamined Patent Application Publication No. 50-1930), and a method for carburizing after a preliminary oxidation under reduced pressure (Japanese Unexamined Patent Application Publication No. 9-324255) are known. Moreover, as a method for producing a carburized part under reduced pressure, a method for carburizing and nitriding in succession in a decompression furnace (Japanese Unexamined Patent Application Publication No. 2006-28541), a method for rapidly carburizing under reduced pressure by using ethylene gas (Japanese Unexamined Patent Application Publication No. 11-31536), and a method for rapidly carburizing under reduced pressure by feeding carburizing gas in pulses (Japanese Unexamined Patent Application Publication No. 2004-332074) are known. Furthermore, as a method for partially carburizing or for partially changing a depth or a concentration of carburization, a method for partially carburizing by using an anti-carburizer (Japanese Unexamined Patent Application Publications No. 10-273771 and No. 4-32537), a method for partially carburizing by using a plating (Japanese Unexamined Patent Application Publication No. 8-60335), a method for controlling a depth of carburization by utilizing a plastic deformation (Japanese Unexamined Patent Application Publication No. 5-25610), and a method for removing unnecessary portions by grinding or cutting after high concentration carburization (Japanese Unexamined Patent Application Publication No. 4-250927) are known.
In gas carburization, an intergranular oxidation layer is formed on a surface of a steel material, and it functions as an initial crack, whereby fatigue strength may be decreased. Moreover, elements effective for quenching are oxidized, and metallic structure is insufficiently quenched, whereby pitting strength may be decreased. On the other hand, carburization under reduced pressure (a vacuum) is a method effective for improving pitting strength because the intergranular oxidation layer is not formed. However, the cost of equipment for reducing pressure is high, and therefore, a method for carburizing as rapidly as possible is required. Properties of some products may be improved by partially carburizing, but both the gas carburization and the decompressed carburization using conventional techniques take substantial amounts of time and effort.